1. Xi’an university of Technology Prof.Dr.Cao Congjun
Offset Printing
Xi’an university of Technology
Prof.Dr.Cao Congjun

2. Feature Dampening solution Indirect printing (blanket cylinder)
Low impression pressure and fast speed
Dot gain
Thin ink layer
Simple technic , low cost

3. Cp.10,11 Offset press
Feeding unit + Printing unit (inking unit + dampening unit )+Registration unit + Delivery unit
The basic of offset press
Sheet-fed offset machine
Web-fed offset machine

4. 1. Feature of offset machine：
a. Dampening solution；
b. Indirect printing (blanket cylinder)
2. Structure：
Feeding unit
Registration unit
c. Printing unit
d. Delivery unit
3. Types：
Flat to round- Flatbed Cylinder Press：Proof machine
Round to round- Rotary Press：modern printing machine

5. structure of printing unit
Inking unit
Dampening unit
structure of printing unit

6. 1 Sheet-fed offset machine
Delivery part
Printing part
Feeding part

7. Sheet conveyance in a sheet-fed offset press in unit design

8. 1.1 Feeding part Feed pile：auto elevator
Re-feeding the paper without stopping the machine

9. Suction head
In the feeder area the sheet is mostly conveyed by suction and friction whereby the top sheet of lifted by suckers.

10. Sheet separation by sucker tilting

11. Suction head part

12. Stream feeder

13. Double Sheet Detectors Fig11.19
Any double or multiple sheets (i.e., two or more sheets
are picked up together and guided to the feed table) must
be detected in good time if subsequent damage is to be
ruled out. As soon as a double sheet is detected in the
feeder, the feeder stops the conveyance of this double
sheet and any following sheets.
In many cases double sheet detectors still operate
mechanically and usually have to be adjusted to the
substrate thickness. They have certain limits with respect
to their sensitivity, as in the case of light-weight
papers. The operation of optical double sheet controls
is very much easier, as they adjust themselves to the material
thickness at the start of the sheet travel.

14. Double sheet detection systems and their applications

15. The Registration Unit
The accurate position of the print image on the sheet
can only be achieved if each sheet is aligned individually
before it enters the press.
During the actual alignment process, the sheet is pushed or pulled with light force against the alignment guides.
Sheet alignment on the feed table at front and side lays

16. Infeed
Infeed systems to the first printing unit
Between the feeder and the first printing unit a section is needed where the sheet is accelerated. The sheet is stopped on the feed table and the sheet is aligned at a
complete standstill. The impression cylinder moves constantly at printing speed.

17. The infeed system now has the task of bringing the sheet, guided accurately in
grippers, up to production speed and passing it on to the grippers of the impression cylinder.

18. Ranger drum, sequence of functions.
a Initial position;
b Gripper swings towards the stationary sheet and grasps it;
c Sheet is slowly accelerated up to printing speed;
d Transfer of the sheet to the impression cylinder with synchronous
movement

19. Sheet Reversal
Sheet turning devices (single-drum system).
a MAN Roland system: The sucker system picks up the rear edge of the sheet, transfers it to the perfecting grippers which then transfer it to the straight printing grippers. The front sheet edge is released first.

20. b Koenig & Bauer system: The rear sheet edge is gripped by the sucker system of the sheet reversing drum and the front edge is then released.
Sucker and gripper system in the sheet reversing drum move towards each other and the sheet is transferred to the grippers

21. 1.2. printing part
Inking unit

22. Ink fountain with continuous ink duct blade and ink fountain screws.
A flexible ink blade can be adjusted at varying distances to the ink
fountain using ink screws to adjust the amount of ink taken out of
the ink fountain.

23. Dampening unit
Conventional offset printing requires a dampening system to supply a very thin film of dampening solution (approx. 2 um) to the nonprinting elements of the printing plate.

24. Dampening system design
a Vibrator-type dampening system;
b Continuous-type dampening system-Dahlgren;

25. c Indirect dampening solution application through the ink roller;

26. d Brush-type dampening system;
e Centrifugal(离心） dampening system

27. Waterless Printing P240
It uses a special silicone-rubber-coated printing plate and special ink.
A special temperature is maintained for accurate transferring of ink to the substrate.
A waterless plate is an intaglio plate with image areas recessed from the surface of the plate.

28. Printing unit
Plate cylinder
Blanket cylinder
Impression cylinder
传纸滚筒

29. Cylinder Arrangement
a. Unit：a unit with three cylinder
b. Combi-satellite：only one impression cylinder
c. Five cylinder two color printing machine
d. Four cylinder B-B P I B
Note：P (印版滚筒) B (橡皮滚筒) I (压印滚筒)

30. 1.3. Delivery
Chain
Delivery
Counter

31. 1.4. Computer control unit Ink adjustment Registration color control
pressure adjustment
Plate changing
Blanket and press cylinder cleaning
Feeder adjustments
Error checking

32. 2 Web-fed offset -Fig.11.37

33. Sections of the Web Offset Press
※Infeed unit
※Printing unit
※Delivery unit
Types of Web Presses
※Blanket-to-blanket web press
※Common Impression Cylinder web press
※In-line web press

34. Components of a Web Press
Roll stand
Splicer
Web tensioner
Dryer and chill rolls
Folding and cutting
Press console

35. 2.1. Infeeding • Clamping the new reel in the chucks（卡盘）.
• Moving the new reel into working position (the new reel is moved to a distance of 1 cm from the expiring
web, which is protected against fluttering摆动 by a support roller).
• Acceleration of the new reel to the circumferential speed of the expiring期满 web.
• On passing the splice marking,

36. • On passing the splice marking, the expiring web is pressed down to the circumference of the new reel
by means of a foam（泡沫塑料/橡皮） roller (formerly a brush). The adhesive end of the new reel sticks to the expiring reel and at the same time the paste seal is broken.

37. • Swinging in the separating knife to cut off the remaining
piece of the expiring web.
• Braking and ejection of the expired reel while the
new reel is active.

38. Splicer
Flying splicer------P255
Zero-speed splicer P256

39. Zero-speed splicer

40. 2.2. Printing
Combi-satellite
B - B

41. 2.3. Drying Drying methods： microwave infrared ray
ultraviolet radiation

42. Fig.
Hot-air dryer for web offset printing presses
(Ecoweb Convertible, Heidelberg)

43. Fig. 2.1-86 Chill roll stand with six chill rolls.
a Chill roll configuration with web travel;
b Chill roll stand (Heidelberg)

45. Folding

46. 3. Technics Preparation Plate installation Pressure adjustment
Printing

47. 平版印刷常见故障
1)印版引起的故障
a. 砂目粗细不当 印刷部分发虚
b. 砂目太细 空白易起脏
c. 版面氧化或沾有油脂 空白起脏
（用浮石棒摩擦去掉脏点，再涂上阿拉伯树胶）
2) 橡皮布引起的故障
a. 高温或橡皮布浸油 橡皮布发粘
（避免高温和浸油，常擦滑石粉）
b. 橡皮布未绷紧 图文重影
c. 橡皮布表面凹陷或衬垫不匀 图文缺陷
（在橡皮布背面进行衬垫修补，对极小部分可以涂松
节油或煤油使橡皮布膨胀）
d. 橡皮布或衬垫滑移 墨色不匀，网点铺展

48. 3)滚筒引起的故障
a. 橡皮滚筒压力过大 版面砂目磨损,图文损伤
b. 压印滚筒压力过大 纸张伸张、褶皱，套印不准
c. 压印滚筒叼纸牙磨损 咬纸不稳，套印不准
4)墨辊引起的故障
a. 墨辊压力过大 造成版面图文部分受损
（用砂纸、浮石磨擦）
b. 墨辊直径不一致 版面着墨不匀
c. 墨辊有杂质或油墨硬化 输墨不良，印品无光泽
5)水辊引起的故障
a. 水斗辊和传水辊接触不良 供水不匀，使墨色变化
b. 水辊绒硬化 磨损印版
c. 着水辊压力过大 磨损印版

49. Homework
P260 review questions 1,4,5,14,15,16,18,20.