一个简化双螺杆旋转食品挤压机：设计，制造和检验外文文献翻译、中英文翻译

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A simplified twin screw co-rotating food extruder: design, fabrication and testing

S.A.M.A.N.S. Senanayake a, B. Clarke b,*

Division of Agricultural and Plantation Engineering, The Open University of Sri Lanka, Nawala,

Nugegoda, Sri Lanka

Department of Postharvest Technology, School of Agriculture, Food and Environment, Silsoe

Collage, Cranfield University, Silsoe, Bedfordshire MK45 4DT,UK

Received 6 July 1998; accepted 10 February 1999

Abstract

A simplified co-rotating twin screw food extruder was designed, fabricated and tested in England,

followed by extensive testing in Sri Lanka. It was built as a model to meet the specific product and

financial constraints of less developed countries and was expected to be used in those countries to

widen the production capabilities of extruded foods. The machine had an estimated delivery of 10

kg/h and was made mainly with mild steel. Two types of screw were made, one with a constant

pitch of 14 mm and the other with varying pitch in segments of 14, 12 and 10 mm. The machine

was powered by a 2.2 kW electric motor with electronic speed control .The machine also had

electrical heating with a temperature controller and a pressure sensing device. The cost of

fabrication of the

machine was estimated at £2000 with most of the parts built in a fairly simple workshop. A

mixture of rice and dried banana was successfully extruded as a potential snack food and on the

basis of maximum expansion the best results was obtained from a barrel temperature of 120°C,

screw speed 125 rpm, feed moisture 15% and with a die orifice size of 3 mm. When the alternative

compress ion screw was tested very similar results were achieved with no significant improvement

Keywords: Twin screw extruder; Design; Low cost; Snack food; Continuous cooker; Local

construction; Cereal mixtures

Nomenclature

a Die diameter (mm)

B Channel width (mm)

C Screw circumference (mm)

d Screw core diameter

D Outer diameter of screws (mm)

H Flight depth (mm)

M Moisture content (% wet basis)

n Number of fight turns

N Speed angular (rev/min)

p Pitch (mm)

Q Delivery rate (mm3/min)

S Total helical length of screws (mm)

t Temperature (℃)

T Residence time (min)

a Overlap angle of screw fights (degrees)

d Calender gap (mm)

e Side clearance (mm)

q Product density (g/mm3 )

/ Helix angle (degrees)

* Corresponding author. Fax: +01525-863277; e-mail: b.clarke@cran-

®eld.ac.uk

PII: S 0 2 6 0 - 8 7 7 4 ( 9 9 ) 0 0 0 4 9 – 7

1. Introduction

Extrusion cooking is finding ever increasing applications in the food process industry. Apart

from providing a means of manufacturing new products, it has successfully revolution is many

conventional manufacturing processes (Harlow, 1985, Frame, 1994). Today, extruders come in a

wide variety of sizes, shapes and method of operation. There are three types of food extruder

found in industry: hydraulic ram, roller and screw type extruders (Frame, 1994). The screw

extruders are very different to the other two having special features such as continuous processing

and mixing ability. Single and twin screw types are both widely used in the food process industry.

Unfortunately, most of the food extruders available in the market are either so costly that less

developed countries cannot afford to buy them except by some form of assistance or outside

investment or else are not appropriate for the wide variety of materials that need to be processed.

As a result the growth of extrusion technology of food into these countries has been hindered

despite its many advantages.

Fig. 2. Plan drawing of the twin screw extruder with drive system. 1-V belt pulley, 2-gear box, 3-

food seal, 4-¯ange clamp bolt, 5-die plate, 6-die, 7-two segments of the extruder chamber, 8-

extruder screw.

were made so that they could be externally screwed to the die plate.2.5. Drive system The machine

was driven by an electric motor of 2.2kW using a twin belt drive between the motor and a gearbox

shown in Fig. 2. The speed reduction in the box was2.08 while an electronic speed controller was

used to control the speed continuously over the range required.

Fig. 3. Front portion of barrel showing provision for heaters, temperature and pressure sensors. 1-

slots for heaters, 2-end flanges, 3-side flanges to barrel, 4-hole for pressure sensor, 5-twin holes to

form the barrel.

2. Motor power

In twin screw extruders the motor power is utilized mainly to compress and shear the food

dough that squeezes through various gaps in the intermeshing screws and the gap between the

screws and the barrel. When dealing with a wide range of foods under different process conditions

the shear resistance can vary widely because of changes in the rheological behaviour which would

prevent accurate estimate of the motor power. Owing to the unknown character therefore of the

novel materials a motor power was selected based on that used for similar materials in similar

sized extruders with a safety margin and from exploratory trials in the Brabender extruder. Rossen

and Miller (1973) give a range of specific energy consumption figures for different extruders

which ranged from 0.02 to 0.10 kWh/kg. At 10kg/h throughput this gave a maximum power

requirement of 1 kW while the Brabender trials tended to indicatea power requirement of about

half of this value. The 2.2 kW, 3 phase AC motor used was amply capable of supplying this power

plus all other drive friction losses.

3. Gear box

In the co-rotating extruder the two screw shafts are driven at the same speed in the same

direction. The main problem is that they are very close together. The gearbox was designed to

drive two pinions, coupled to the shafts by shear pins, by using a gear wheel of more than double

the width of the pinions. In this way the two pinions could ®t side by side driven simultaneously

and maximise their diameter space as shown in Fig. 2. Lubricated phosphor bronze thrust bearings

were used to resist the axial load generated by the material along the shaft.

2.6. Heating and temperature control

Heating of the barrel to give necessary thermal input for cooking the food was done by two sets of

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摘要：

Asimplifiedtwinscrewco-rotatingfoodextruder:design,fabricationandtestingS.A.M.A.N.S.Senanayakea,B.Clarkeb,*DivisionofAgriculturalandPlantationEngineering,TheOpenUniversityofSriLanka,Nawala,Nugegoda,SriLankaDepartmentofPostharvestTechnology,SchoolofAgriculture,FoodandEnvironment,SilsoeCollage,Cranfie...

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