surface engineering paper

8/6/2019 Surface Engineering Paper

1/20

SURFACE ENG INEERING FO R LO O K & FEEL

E.M. Kuiper

N. Peeters

October 200 8


2/20

2 Surfa ce Engineering | University O f Twente

TABLE OF CONTENTS

Introd uction ..........................................................................................................................................................................................3

Prob lem def enit ion ............................................................................................................................................................................4

Theory ..................................................................................................................................................................................................5

Method .................................................................................................................................................................................................6

Practice ................................................................................................................................................................................................8

Results ...................................................................................................................................................................................................9

Conclusion ......................................................................................................................................................................................... 12

Red esig n ........................................................................................................................................................................................... 13

Liter a ture .......................................................................................................................................................................................... 20


3/20


INTRODUCTION

A pan is a product in which grip plays an important role in terms of safety and comfort. The grip on the handleneeds to be good enough to prevent any accidents caused by slipping hands from happening. Therefore not only

the shape of the handle is important but also the surface. It should be rough enough to provide sufficient grip and

smooth enough to ensure comfort.

The problem definition will contain the detailed problem description. The problem definition will end in a research

question fo r the f urther r esea rch.

A literature study will give a background of grip and friction of different materials; like metal, plastic and wood.

After the literature study the theory will be tested in practice. First a method will be created to test some aspects

of the theory. On the basis of this method the practice will be executed. After discussing the results, these results

will be used for the redesign of the handle.


4/20


PROBLEM DEFENITION

Some pan handles are better than others. For this research a handle was found that wasin need of some improvement. To find and select this handle a series of test were

conducted. The temperature of the handle was measured while cooking water and the

relative grip with dry and wet hands was estimated by hanging a five kilogram weight

from the panhandle. Figure 1 gives an example of this experiment.

These results have been used to quickly asses the price quality ratio of the different

pans, where quality is assessed as the amount of grip the handles provide. From these

results it appeared that the grip of a certain Tefal frying pan was relative poor

compared to its price. This pan is thus chosen as a subject for further studies and

red esign by surf ace engineering to improve g rip.

This can be summarized in the following research question;

How do the current surf aces of the Tefa l pa n look like and how can these surf aces

be altered to improve grip and maintain a similar look.

Figure 2 shows the Tef al f rying pa n which will be used f or f urther research.

Figure 2: Tefal frying pan

Figure 1: Testing


5/20


THEORY

In ea rlier studies research was done concerning the static fr iction at the hand/ handle interf ace [1 ]. An overview ofthe results can be found below in figure 3. In this figure MVC is the Maximum Voluntary Contraction measured

with an EGC. EMG or Electromyography gives the absolute value of the force exerted on a handle.

Figure 3: Static friction

From this research it appeared that the best grip was conceived when stainless steel was used. But this is only

valid in wet and dr y condi tions. If lubrication is used like soap the conventional stainless steel surf ace d oesnt give

as much grip as possible. Texturing the surface will improve the lubricated grip, but decreases the normal dry

grip.

According to another study [2] this is caused by hydrophilic and hydrophobic effects of these materials. In

essence, the friction of skin increases when the skin is wet. This increase can be ascribed to an increase in the real

area of contact resulting from the specific effects of water plasticization on the epidermis. The epidermis tends to

ge t sof ter and more f lexib le d ue to t his ef f ect. But the conclusion that wet skin alwa ys increa ses the f riction is not

true. Another eff ect of wa ter is lubrication and hyd rophilic materials for m a more stab le lay er of wa ter moleculesreducing thus the friction. On the other hand, hydrophobic materials allow the skin to get wet but prevent the

formation of a stable lubricating water layer.


6/20


METHOD

As stated before grip and heat build up are the main subjects for this research and redesign. In order to quantifydata from the preliminary research a more scientific approach was chosen. This research was conducted in two

separate experiments, one for temperature or heat build up and a second one for investigating surfaces of

different materials with different finishes. In the first only the current situation will be analysed whereas in the

second experiment also alternative materials get a closer look. This is done because the heat temperature

distribution and heat build up is depending on geometry and design of the overall construction and is harder torep licate w ith diff erent materials.

Te m p e r a t ur e a n d h e a t b u i ld u p

For this experiment the research question was how temperature changes in the different materials of the pan

handle when the pan remains at the same temperature. Of course the temperature of the pan needs to be

significantly higher than the ambient temperature, but also constant during the experiments. To accomplish this, the

pan will be filled almost to the top with 1 litre of boiling water from a water cooker and kept boiling at the

furnace.

Now with the pan at a constant temperature it is important to monitor its temperature over time. Therefore a

thermocouple thermometer will be used which will be attached to the pan handle and at certain time intervals the

temper ature will b e noted using the scheme below in Figure .

time (s) 0 30 60 90 120 150 180 210 240 270 300

Tmetal (C)

Tplastic (C)

Figure 4: Measuring table

Since only one thermometer is available the experiment will be conducted twice, measuring the different

mater ials. The time will be kept w ith the use of a stopw atch.


7/20


Sur f a ce s t ructure

In order to quantify surface a spectral analyses will be made of the different materials using a specialized

microscope. Several samples are made from different surface finishes and different materials as well as the

current pan handles.

This spectrum analyses results in a set of data from which a three dimensional image of the surface can becreated using the microscopes software 123. The area that is analysed has a surface of roughly 500m by

500m. The peaks and dents can be highly exaggerated to make them visible. The program interface and the

adjustable variables are shown in Figure 5.

Figure 5: the 123 microscope control program


8/20


PRACTICE

W ith the f unctional te sts de scribed ea rlier o n in the method section more insight wa s ga ined re ga rd ingtemperature increase of the handle materials as well as surface structures of the currently used materials and

pro posed alternatives.

H e a t a n d t e m p e r a t u r e

In practice there were a few problems regarding measuring the temperature. At first the pan handles

temperature increased due to holding the pan and placing it on the furnace. It was also difficult to keep the

thermometer at the same spot. This was later on solved by taping it to the handle. Also little drops of boiling

water on the thermometer and panhandle influenced the first attempts to measure the temperature.

Sur face t ex tu re

W ith the use of a microscop e and moir interf erence pa tterns a 3 D image of the surfa ce of the handle and

several other materials were made. Due to the metallic transparent coating on the plastic parts of the handle

making a straig ht forw ar d surf ace imag e wa snt po ssible. W ith the use of spe cial two component rubb er, with a

resolution of 0.1m, a nega tive mould w as mad e f rom the surfa ce and then ex amined unde r the microscop e.

The analysis of the surface texture of wood was made with the use of the same two component rubber.

Unfortunately the rubber sticks to the wood sample, so it wasnt possible to make reliable analysis. Hiziroglu

(2007) [3] made 2D surface texture analysis of different wood samples with the use of a stylus method. Figure 6

shows the roughness of three typ es of w ood; p articleboard , overlaid pa rticleboa rd and hard boa rd. These typ es

of wood cannot be used for the redesign of the handle, because of the composites and the non-water resistants

of the material.

Figure 6: Roughness profiles of wood samples


9/20


RESULTS

Results of these tests were collected, visualised and analysed in several ways.

H e a t a n d Te m p e r a t u r e

As can been seen from the test results temperature rise in the metal parts of the handle arent a real problem. In

fact, temperature drops in time. This is probably due to the fact that the handle was still warm from body heat

and holding the handle. But since temp era ture d ecreases in a p eriod of 5 minutes it is unlikely it w ill ra ise a f ter 1 0

minutes. See figure 7.

Figure 7: Temperature diagram of the handle

The plastic handle parts formed a heat buffer between the boiling hot pan and the thin metal inlay at the top of

the handle. Another aspect that pr events the user fr om burning his hand is the f act that the metal inlay is very thin

and thus the heat capacity of the inlay is very low. Although heat is conducted very rapidly by the metal, the

amount of heat is very low preventing the user from neither burning his or her hands let nor feel the temperature

of the metal inlay .

Sur face t ex tu re

The results from the surface scan are several 2D and 3D images. Figures 8 and 10 below shows at the surface of

the plastic handle parts and figures 9 and 11 shows the surface of the polished metal inlay. Compared to the

surfa ce on the rig ht side fr om the metal inlay , the p lastic is very rough.

These imag es wer e compar ed with the results f rom samp les that had other surfa ce trea tments. Figure 1 2 shows

the surfa ce of pla in rolled stainless steel. O n the r ight side, f igure 13 , is the surfa ce of a pie ce of stainless steel

that was sanded with a 320 grain.


10/20


Figure 8: Handle plastic 3D Figure 9: Handle RVS 3D

Figure 10: Handle plastic 2D Figure 11: Handle RVS 2D

Figure 12: RVS rolled 3D Figure 13: RVS sanded 3D


11/20


Figure 14: RVS rolled 2D Figure 15: RVS sanded 2D

Figure 16: Handle plastic profi le Figure 17: Handle RVS profi le

Figure 18: RVS sanded profil e Figure 19: RVS rol led profil e


12/20


CONCLUSION

The first conclusion that can be made is that although the thermal resistance of metal is low and heat is conductedin a high rate the amount of heat that could be transferred from the metal to the hand of the user is limited due to

the low heat capacity. Therefore heat wont be an issue if nothing changes in the dimensions of the metal inlay.

Also the temperatures to be deled with are way below body temperature and thus of no real significance. Of

course, that is this pa nhand le, wherea s f or o ther p anhandles this might very well b e a may or issue.

From the surface research the conclusion can be made that the polished metal inlay is by far the smoothes surface.

From earlier studies it was know that smooth surfaces have better dry grip compared to the grip on rough

surfaces and that wet hands improve grip overall. Therefore in the handle that was examined the metal inlay

provides the dry grip and the plastic parts serve as a heat buffer. The use of two materials is in fact very clever.

So to improve g rip the metal should b e smoother and p refer ab le of a hyd rophobic materia l.

Only when surface textures exceed the microscopic level they improve grip. But in that case other effects comeinto play where terms like friction are of less importance.

One of the first ideas was to sand the metal part to improve the wet friction, but this has a negative influence on

the dry friction and the surface roughness is doubtfully large enough to rely on other grip mechanisms than just

friction. Another suggestion was to make the metal inlay not from polished stainless steel but instead of chromed

metal, since this is supposed to be much smoother. Then again, from earlier research it shows that chrome has a

relative low dry grip and relative high dry grip. So the application of chrome is possible but the dry friction has

to come from the plastic parts of the handle. Afterwards it would have been interesting to also examine the

surface of a chrome sample and compare it with the polished stainless steel.

The conclusions made above will be used to develop several concepts in redesign.


13/20


REDESIGN

From the conclusions made based on the experiments there are a set of new design requirements.

- The new panhandle has to have a similar configuration with the metal inlay to prevent any burns.- The handle has to has a smooth surfa ce in order to g ive suff icient dr y gr ip- The handle has to be made from a hydrophobic material or has to have a hydrophobic coating with the

same chara cteristics.

- Macroscopic textures can be added for look or feel and to improve grip with other mechanisms thanpure f riction. This could also be a top ic for f urther r esea rch.

C o nce p t g e n e r a t i o n

For the redesign of the handle combinations of two applicable materials were made, mainly focusing on wet and

dr y gr ip. This results in three dif f erent concepts. These concepts wer e d eta iled and rep resented be low.


14/20


CO NCEPT 1: CHROM E

- W et g rip: chrome inlay with hyd rophobic coating- Dry gr ip: super smooth pla stic

The chrome is in fact a stainless steel part with chrome plating as a surface finish and a hydrophobic coating like

Duralon from the German company Cotec. This results in a handle as shown below.

Figure 20: The chrome concept


15/20


For the plastic part a plastic with a good hardness and strength is used which is polished after injection moulding.

W ith the use of the mate ria l selection pr og ra m CES po lymers and ela stomers wer e exa mined by their hea t

resistance and price. See figure 21 below.

Figure 21: CES melting point vs. price graph

From this the choice w as made fo r Polyethylene which is go od moulda ble and has a high melting temp era ture a nd

is relative cheap.


16/20


CO NCEPT 2: SAN DED

- W et gr ip: smooth pla stic with hyd rop hobic coa ting- Dry grip: sanded stainless steel and smooth plastic

The wet gr ip comes from the same d urab le p olye thylene as in the chrome concept w ith a high hard ness which ge tspolished after injection moulding and a hydrophobic coating like Duralon from the German company Cotec. Dry

grip comes from the sanded stainless steel where other mechanisms than friction act as well as from the plastic

handle. Two renderings are made with different orientation of the sanded steel. These will be later assessed by a

consumer audit.

Figure 22: The sanded concept


17/20


CO NCEPT 3: RO UG H

- W et g rip: p olished metal a nd textured pla stic (perhap s only b ottom surface)- Dry g rip: polished metal

The polished metal is a similar stainless steel inlay like the current frying pan has. The surfaces of the plastic partsof the handle are provided with rough like structures relying on other grip mechanisms than friction and is build-in

in the mould. The pla stic pa rt of the handle is mad e f rom the same po lyethylene a s the other to concepts.

Figure 23: the rough concept


18/20


Concept se lec t ion

Although all concepts are developed in such a way that they all provide excellent grip, some of them look very

smooth and slippery. So concepts are assessed based on if they look;

- ComfortableBoth the chrome and sanded concept look very comfortable. The textured

pla stic of the rough concept looks a little less comfor tab le.

- Suff icient gripAll concepts are thus developed that they provide sufficient grip under

wet and dry circumstances. Apart from that the chrome concept has a

very smooth look and therefore cannot convince the consumer of the great

amount of grip it is pr oviding.

- DurableIn the case of durability one could argue that all three concepts are made of the same basic materials and are

thus all even durable. Apart from the coating this is true, but even the coating has a high durability and good

resistance according to Cotec. Unfortunately this couldnt be assessed further with programs like CES since they do

not provide the op tion to sort f or hydr ophobic prop erties.

- Tefa l p rod uctSince the products did not change that much either concept has the

Tefal-look. Only the rough concept does not emit the quality Tefal

stands for. The high quality finish looks of the chrome and thesand ed scores be tter in this ar ea .


19/20


Overall the sanded concept scores best on almost any area. Therefore this is the chosen concept and will be

pro posed as the impr oved red esign of the Tefa l fr ying pa n.


20/20


LITERATURE

[1] O mear a D.M. and Smith R.M, 20 02 , Functional handgrip test to determine the coefficient of static friction

at the hand/ handle interf ace.

[2] Ada ms, M.J. and more, 20 07 , Friction and lubrication of human Skin.

[3] Hizirogly S. and Zara te S, 20 07 , Mechanical Properties and Surf ace Characteristics of Colombian W ood

Composites.

surface engineering paper

Documents